1. Field of the Invention
The present invention relates to rare earth-cobalt permanent magnets. More particularly, the present invention relates to rare earth-cobalt magnets which do not contain samarium as an essential component.
2. Description of the Prior Art
Many permanent magnetic compositions are known which are based on a mixture of at least one rare earth metal and cobalt. However, of all of the type of rare earth-cobalt magnetic compositions, those which contain samarium optionally with or without the presence of another rare earth metal, are the most useful commercially. The principal drawback to samarium containing compositions is the high cost of producing samarium metal. However, the state-of-the art is such that only rare earth-cobalt magnets which contain samarium have had sufficient coercive force to enable the use of the magnets as high strength permanent magnets. The following prior art references show rare earth-cobalt magnet compositions many of which are samarium containing compositions:
Ostertag et al U.S. Pat. No. 3,421,889, Nesbitt et al U.S. Pat. No. 3,560,200, Cech U.S. Pat. No. 3,826,696, Martin U.S. Pat. No. 3,887,395, Smeggil et al U.S. Pat. No. 3,892,601, Strnat U.S. Pat. No. 3,998,669, and Sagawa et al U.S. Pat. No. 4,047,982, Buschow et al U.S. Pat. No. 3,523,836 show a rare earth-cobalt based composition in which the rare earth component is a combination of lanthanum and cerium, while Tawara et al U.S. Pat. No. 3,839,102 show a composition based upon a combination of cerium with cobalt and copper. The Tawara et al reference U.S. Pat. No. 3,947,295, Menth et al U.S. Pat. No. 4,082,582 and Yamanaka et al U.S. Pat. No. 3,982,971 all show multi-component magnetic compositions which contain at least samarium, copper, cobalt and iron.
Ratnam and Wells, Proc. Conf. AIP, Magnetism and Magnetic Materials, 18(2), 1973 pp. 1154(58), have shown a magnetic composition in which from 6 to 9 wt.% samarium was added to mischmetal-cobalt alloys while Benz and Martin, Cobalt-Mischmetal-Samarium Permanent Magnet Alloys: Process and Properties, J. Appl. Phys., 42, 1971, 2786(89) have reported mischmetal-cobalt-samarium magnetic compositions which contain up to 18 wt.% samarium. Still other reports show alloy compositions in which iron and copper have been added to various rare earth-cobalt alloys prepared by casting techniques. (Nesbitt et al, J. Appl. Phys., 40, 1969, pp 4006(09) and Tawara et al, J. Appl. Phys., 7, 1968, p 966). However, the properties of these as-cast, copper containing magnets are not as sufficient as desired, and sintered SmCO.sub.5 has found favor instead. Still another type of sintered magnetic material which has been investigated is a cerium-cobalt-copper-iron alloy as described by Tawara et al, IEEE Tans. Magnetics, v. MAG-8, 1972, pp 560(61). However, the process for producing the magnetic alloy requires a post-sintering aging treatment at a temperature between 300.degree. and 400.degree. C. for minimum of three hours in order to increase the intrinsic coercivity to a maximum value of 7,000 oersteds. However, the magnetic alloy of the present invention possesses a substantially higher intrinsic coercivity of about 28,000 oersteds, which is equaled only by Sm-Co magnets, than the alloy above. Moreover, the high intrinsic coercivity properties are induced in the present alloy by a significantly simpler procedure which does not require an aging cycle.
Therefore, a need continues to exist for a magnetic alloy whose magnetic properties are at least as good as samarium based alloys but yet which is not based upon samarium.